The creation of turbulence within a fluid stream has many industrial applications. For example, the creation of turbulence generally enhances the mixing of two fluid streams. The mixing of fluids has applicability to a wide range of industrial processes including for example burner designs that rely on the mixing of a fuel with air. In such burner designs, as well as many other industrial processes that rely on the mixing of two fluid streams, the mixing of the fluid streams may be achieved or enhanced by channeling the streams through a static mixer. A static mixer typically includes one or more baffle plates or other similar elements that create or generate turbulent flow zones within the static mixer that facilitate mixing of the fluid streams.
The creation of turbulence within a flow stream may also be desirable in applications where contact or near contact between a fluid and a surface results in some benefit. By way of example, heat exchangers generally rely on the contact or near contact between a fluid stream and a surface to effectuate heat transfer to or from the surface via the fluid stream. One such heat exchanger is a shell-and-tube heat exchanger wherein one fluid stream flows through one or more inner tubes and another fluid stream flows through an outer tube or shell containing the inner tubes. Heat transfer between the two fluid streams is across the wall on the inner tube(s) and thus contact or near contact between the fluid streams and the wall of the inner tube(s) enhances heat transfer therebetween. In this regard, shell-and-tube heat exchanges may include one or more baffle plates or other similar elements (typically on the shell side of the heat exchanger, for example) that create or generate turbulent flow zones within the heat exchanger that enhance heat transfer between the fluid streams.
One particular industrial application where creating turbulence so as to bring a fluid stream in contact with or adjacent to a surface occurs in the water treatment industry. In this industry, for example, ultraviolet light reactors are used to treat contaminated water. Typically, ultraviolet light reactors include an inner tube and an outer tube concentrically disposed about the inner tube. A UV light source is typically disposed within the inner tube and the inner tube is formed from a suitable material that allows UV light to pass therethrough. Contaminated water flows through the passage between the inner and outer tubes and is exposed to the UV light to effect treatment of the water.
One or more baffle plates may be located along the axis of the reactor. In conventional designs, the baffle plates are configured as generally flat or planar disc plates having an outer periphery and an aperture formed therethrough that defines an inner periphery (e.g., a washer). The planar disc plates are positioned so that the outer periphery engages the inner surface of the outer tube and the inner tube is disposed through the aperture such that the outer surface of the inner tube is adjacent, but spaced from the inner periphery in the plate to form a gap therebetween. In this way, as the contaminated water flows along the passage between the inner and outer tubes it has to pass through the gap between the inner tube and inner periphery of the baffle plate(s). The reduction in cross-sectional area as the water flows through the gap results in an increase in the local fluid velocity of the water. When this relatively fast moving fluid contacts the relatively slow moving fluid behind or downstream of the baffle plate, the shear created by the differential velocity forms toroidal vortices (e.g., similar to smoke rings) that move in the downstream direction.
While generally successful for certain water treatment applications, there are a number of drawbacks to conventional ultraviolet light reactors that limit their use in a broader range of water treatment applications. For example, the ultraviolet light reactors are generally effective for high UV transmittance fluids but lose their effectiveness as the ability of the UV light to penetrate the water diminishes. Accordingly, ultraviolet light reactors are most effective for water with low solids content. For water with relatively high solids content, the UV light will penetrate into the fluid only a short distance (as little as 0.1 mm in some applications). Thus, some of the water borne particles may have little or no exposure to the UV light. For effective treatment in these high solids content applications then, it is necessary to bring the water borne particles near the inner tube from where the UV light emanates.
Planar disc plates as described above and the toroidal vortices they generate provide relatively low improvement to the treatment of high solids content contaminated water. In this regard, it is believed that toroidal vortices are relatively unstable and do not permit different water borne particles to enter and leave the toroidal vortex as it moves downstream. As a result, relatively few water borne particles are brought into proximity to the inner tube, even though turbulent vortex generation occurs. Moreover, because relatively few water borne particles are brought into proximity to the inner tube, effective treatment of high solids content water via UV treatment may not be achieved.
In addition to the above, planar disc plates are often currently utilized in ultraviolet light reactors to direct at least a component of the fluid flow transversely across the inner tube. Such transverse flow results in a lateral loading force and associated bending moments on the inner tube. In current designs, the inner tubes are typically formed from rather brittle quartz tubes that are susceptible to fracture induced by the bending moments. As a result, attempts to increase the turbulence and vortex shedding to improve water treatment by increasing the flow rate through the reactor is limited by the allowable bending stress limitations of the inner tube.
Accordingly, there is a need for an improved baffle design and apparatus utilizing such baffles that address these and other drawbacks of existing devices.